EEVblog Electronics Community Forum
Electronics => Repair => Topic started by: PaulAm on February 02, 2017, 11:06:37 pm
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I'm repairing an old HP DesignJet plotter and I have an unreadably dim VFD display. I had a used replacement, which is at least readable, but it's still not as bright as I'd like.
This is a Futuba US202SD01A display which is a 2x20 VFD with the associated support circuitry and uses a 5 pin serial interface connector. Apparently, somebody has reverse engineered the protocol and there's a library available to drive the display from an Arduino, but I'm coming up blank on a display replacement.
Anyone have a NOS unit gathering dust? Maybe just the VFD? Doesn't look like fun to remove and replace it, but it's doable.
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I replaced mine with a 2x20 LCD but there are "issues" with special characters and it most certainly won't work with anything other than English. That Futaba display has a plethora of special characters and you only have space for 8 in the LCD. I toyed with a dynamic loader to load them as needed but it was more hassle than it was worth.
I reverse engineered the protocol and wrote a converter for the Parallax Propeller. That was years ago now, I'll have a look and see if I can find the code. It's a funky protocol.mfrom memory it starts out 8 bit and then switches to a 10 bit stream after boot up.
I had no luck sourcing credible vfd replacements.
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2x20 VFDs are fairly standard, you may be able to transfer the glass from a similar display to the board on yours but beware some of the modern ones are "chip on glass" with an internal driver.
You can also rejuvenate VFDs, have a look online. Essentially you boost the filament voltage to burn off contaminates and expose a new layer of emissive oxides, similar to rejuvenating tired CRTs. VFDs are essentially inside-out flood gun CRTs.
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Well some more looking and I found some NOS Futuba NA202SD08FA displays which appear to use the same display and the same driver chips. I have a couple on order and we'll see if they work out.
This display has all the leads on one side.
An alternative would be to get a current display and put in a protocol converter, but that's more work than I really want to do. Transferring the display will be bad enough.
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Have you tried rejuvenating it? I found the page I was thinking about, turns out it's right here on eevblog.
https://www.eevblog.com/forum/chat/vacuum-fluorescent-display-rejuvenation/ (https://www.eevblog.com/forum/chat/vacuum-fluorescent-display-rejuvenation/)
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I'll give it a shot and see what happens; it might be good enough.